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Unread 09-26-2012, 09:16 PM   #16
ZeeJay1997
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OP, out of curiosity is this the fix you paid 20 bucks for?

1. Find the PCM, ECM, ECU. and pull the plugs off. Disconnect the battery first.
2. Spray Electronic contact cleaner in and on all plug contact area and PCM contact area. Allow to dry for 4-8 minutes.
3. Put Dielectric Silicone Compound on all contact areas and plugs.
4. Plug back in firmly.
5. Remove the two screws just below the 3 plugs one at a time and put three 4 mm washers on the screw and put it back. To prevent screw from touching circuit board and shorting it out.
6. Put Zip Tie on to secure the connectors and prevent vibrations. 2 per plug

If so, you could have got for free here. Unfortunately, this is not a permanent repair and the washers under the screws don't do anything aside from disturbing the area of the loose solder joints and in order to get the screws out, the plugs have to be taken loose, which has the same affect as removing screws and adding washers.. Not that it's a bad repair, but not the best solution and i hate you had to waste 20 bucks.

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Unread 09-27-2012, 01:50 AM   #17
Uniblurb
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Quote:
Originally Posted by cherub2him View Post
@Uniblurb: where is this PCM ground on the coil stud exactly?? Is it behind the PCM? I'll def take a look at that one. I checked the vacuum hose for leaks by just kinda nudging it while the engine idled but nothing happened. I guess that means it's ok I suppose? Something I found very interesting though is that when I accidentally rolled up my windows and just held the switches up, the engine idle really dropped. Released it--went back to normal. I'm thinking an alternator issue? when I had it checked a month ago, the guy said it was low but not in dire need of replacement. And you're right man, Zeejay's 12 points is def good stuff. I've read it before . Until you said that though, it didn't dawn on me that THE Zeejay97 was in this thread!
There's a wiring harness which runs forward along the passenger side of the engine from the large wire harness next to the firewall. There are 3 ground wires coming out of this harness with one on the oil dipstick tube brace stud and 2 on the ignition coil studs which hold the coil on. This is right next to the motor mount and the one up against the mount is hard to get off but can be done with a 1/2" open end wrench.

On mine the ground on the dipstick tube bracket stud was covered with oil and may not have been all the way tight. But the PCM ground is on one of the coil studs and both of the studs/wire eyelets were rusted/corroded. Sprayed them down heavily with PB first and then you have to remove them from underneath. There's nuts against the coil bracket itself, then the wire eyelets, then nuts on top of those. Everything is 1/2" so I had to slip a thin 1/2" open end wrench on the nuts against the coil bracket and then another 1/2 wrench on the outside. You can use a 1/2" socket on the front coil stud but not on the one against the motor mount. To make matters worse I had to use a pair of vice grips on the wire connectors to hold them in place while turning the nuts since everything was seized together. I also removed the studs altogether and cleaned where they go into the block behind the coil. But it was worth it.

You won't see a separate wire ground on the outside, or going to the inside, of the PCM itself since it's grounded through one of the pins in the connectors from the engine ground wire just mentioned. Believe that's the way it works.

In addition to the one and only ZeeJay1997 in this thread you also have JS97ZJ who "wrote the book" in rebuilding 96-98 PCM's.

http://www.jeepforum.com/forum/f13/9...tures-1303589/

BTW, on checking for vacuum leaks you can spray carb cleaner on the different connections with the engine running to see if the rpms change. Some suggest using propane or starting fluid but this is pretty dangerous since they're so flammable and only do this on a cold engine.

My engine rpms just decrease slightly when the windows bottom up/down and still holding the button. Don't believe this is a real problem. You should have good alternator contacts and remove them to clean them up.
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-Stalling ZJ? 12 things to check before replacing a sensor; the Dirty Dozen
-Crankshaft position sensor multimeter test. & video of testing.
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Unread 09-29-2012, 10:06 PM   #18
Slyfox3453
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THIS WILL WORK! It is a 10 cent problem!!! On your pcm, there are 2 screws on the front plate. They are to long so they short out the board. I screwed mine half way out. And my jeep is running better than ever. My jeep would sputter to a stop when idling at stop signs and even died on me going 30 or higher. I found out the pcm has those two screws that were to long. I was going to spend 400 bucks on a new pcm. But read a few threads.
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Unread 09-29-2012, 10:37 PM   #19
ZeeJay1997
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Quote:
Originally Posted by Slyfox3453 View Post
THIS WILL WORK! It is a 10 cent problem!!! On your pcm, there are 2 screws on the front plate.
Baloney! Just because you got lucky doesn't mean it is a fix. It does nothing but postpone either replacing or repairing the PCM.
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Unread 09-29-2012, 10:46 PM   #20
stojakovic
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Quote:
Originally Posted by ZeeJay1997 View Post
Baloney! Just because you got lucky doesn't mean it is a fix. It does nothing but postpone either replacing or repairing the PCM.
Agreed.
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Unread 09-30-2012, 07:58 AM   #21
JS97ZJ
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Quote:
Originally Posted by Slyfox3453 View Post
THIS WILL WORK! It is a 10 cent problem!!! On your pcm, there are 2 screws on the front plate. They are to long so they short out the board. I screwed mine half way out. And my jeep is running better than ever. My jeep would sputter to a stop when idling at stop signs and even died on me going 30 or higher. I found out the pcm has those two screws that were to long. I was going to spend 400 bucks on a new pcm. But read a few threads.
Those screws don't even come close to contacting any electrical connections or the circuit board. This problem has been identified and fixed.

http://www.jeepforum.com/forum/f13/9...3589/...:rtft:
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Unread 09-30-2012, 01:46 PM   #22
cherub2him
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@ZeeJay1997: Yep that is exactly what I paid for. Man, wish I could have found it on the threads here first... :/ O well. I made a mod to it though by wrapping the screws with a decent amount of electrical tape. I figured that since there was a low possibility of the screws actually hitting the PCM and shorting it out, there had to be some other kind of grounding going on that still dealt with the screws. I haven't seen the inside of the PCM so this is just my hypothesis and my associated reasoning:

Since the screws probably weren't hitting the board itself, there had to be an electrical jump toward the path of least resistance (the screws). Given that the distance between the board and the screw was most likely very small (I would have to say less than a 1/8 inch but could even be greater) this is a probable dielectric jumping situation. The air between the screw and the point on the board where the electricity jumps has a dielectric capacity of 1. As the air heats up, the density of the air in that pocket lowers and as such the dielectric value of that space becomes closer to that of a vacuum, which is zero.

In a vacuum if you have two plates connected to a end of a battery, electricity will freely flow between the plates in the vacuum. For reference <http://www.youtube.com/watch?v=XU8nMKkzbT8>. Since the dielectric resistance of the air is less than normal when heated, there are certain times when the flow of electrons through the board will "jump" to the the screw to be grounded since the path of resistance through the air is less than that of the circuit board and electricity always seeks to go through the path of least resistance. Thus a grounding takes place. The screw is in contact with the PCM shell which can act as a ground in this situation. By putting electrical tape on the end of the screws, this entirely elminats the screws from holding a possible charge point that the electrons in the board could jump to when the path would allow for jumping.

This would match up with the times it stalled on me most which were in the morning after I had driven 20+ minutes, and then on my way home at 4:30 after the car had been out in the sun all day. I still need more data though and also a good look at the inside of the PCM itself. This of course doesn't eliminate the solder idea at all as being a valid problem. There are probably a few different problems going on that individually cause the problem one time and that combine and cause the problem at other times. The fact that I have now been 11 days of driving without stalling once after doing the mod gives very strong evidence that the screws were one of the problems. Again, I hadn't been stall free for a month plus before the mod. On one particular day before I took it to the mechanic, It stalled on me 5 times in 30 mins on my way home. The disclaimer to this is that I have no idea what the inside of the PCM really looks like. Even from JS97ZJ's pics, I can't tell if the screw just goes into gel or if there is an air pocket between a bare part of the board and the end of the screw. If the screw goes into the gel and the gel does have a dielectric capacity (higher than that of air obviously) as it should....maybe the screw is hitting an expanded gel and electricity is being conducted to the screw. I don't know, but that's my best guess with what I've got. If someone wants to send me a "broken" 96 ZJ PCM, I would be more than happy to investigate this particular hypothesis, lol.
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Unread 09-30-2012, 02:25 PM   #23
JS97ZJ
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Your getting too scientific. The potting compound (jell) exists in an invironment that goes from however cold it gets in your location (subzero) to around 250* F. This expansion and contraction of the jell pulls on that big connector causing the pins soldered to the board to come loose. The problem will usually get worse as the outside temps start to go down in the low 40's.

Trust me. It's not the screws. I wouldn't have posted that write-up if I had any doubt.
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Unread 09-30-2012, 02:32 PM   #24
ZeeJay1997
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It's not that complicated. The screws fits entirely into a hole in a non conductive composite molding. There is no air gap. They serve to hold a connector together that joins the sub-module (for lack of a better term) to the main body of the PCM.

In other words, The metal plate directly under the main 3 connectors has circuitry mounted on the backside and can separate from the main body. These two screws have to come out (and tabs have to bent back) before this can happen.

As i said earlier, the process of moving things around to loosen the screws causes the elements of the solder joints inside to reposition themselves and fool you into thinking that the act of turning the screws counterclockwise has a positive effect on the driveability of the vehicle.

Dont drink the koolaid
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Unread 09-30-2012, 02:45 PM   #25
JS97ZJ
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^^^^^^^^^^
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Unread 10-01-2012, 10:42 AM   #26
Slyfox3453
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So where is the fix to the problem? The link wasnt complete
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Unread 10-01-2012, 10:47 AM   #27
Slyfox3453
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Well **** guess i have to clean the grounds. Thanks for the help. Lol My theory about the screws crashed and burned. Ill keep reading up on things before i post anything. Lesson learned. Sorry for the misinformation.
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Unread 10-01-2012, 10:03 PM   #28
Uniblurb
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JS97ZJ's full link to his thread was posted on the 1st page and the smiley must have interfered with it the 2nd time around.

http://www.jeepforum.com/forum/f13/9...tures-1303589/

Hey, when I 1st joined the forum I also thought I found the "2 screw fountain of PCM youth" fix on the net. But I was lucky enough to bring it up in a PM rather than on the open forum. I'm sure we'll get over it if you do.
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-Stalling ZJ? 12 things to check before replacing a sensor; the Dirty Dozen
-Crankshaft position sensor multimeter test. & video of testing.
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Unread 10-02-2012, 06:48 AM   #29
Timbone1343
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I had a similar issue and thought it was my pcm for the longest time. Turned out the connector on my coil was loose. I popped the connector apart, pinched them a bit and they have worked fine since, no stalls for almost 9 months.. Knock on wood.

The best way to test it is to start the jeep and twist the connector a little bit then jiggle it up and down a bit. Twisting is what did it for me but some say jiggling did it for them.

Honestly though, it's easy enough to pop the connector apart and pinch them a bit that it's worth trying even if it doesn't stall when you twist/jiggle them.
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Unread 10-03-2012, 10:08 AM   #30
Slyfox3453
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Lol yea. Im not mad. I know how it is lol. If im wrong i would hope someone would correct me.
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